2. SUMMARY Most indicated preterm deliveries occur due to ischemic placental diseases such as preeclampsia (PE) and intrauterine growth restriction (IUGR) (1-4). The maternal-fetal interface in these conditions is characterized by a set of placental findings collectively referred to as maternal vascular malperfusion (MVM) (5-7). This typically involves either impaired invasion and remodeling of maternal spiral arterioles, resulting in diminished placental perfusion (5, 6, 8-17), and/or impaired villous development, compromising establishment of an efficient maternal-fetal transport interface (5, 6, 18, 19). We and others have shown that environmental factors such as oxygen tension can modulate placental development and contribute to ischemic placental disease processes via modulation of Hypoxia-inducible Factor (HIF)-dependent gene expression (10, 20-31). An unparalleled opportunity to study environmental effects on embryonic and placental development occurs during in vitro fertilization (IVF). We have shown that IVF has significant effects on blastocyst gene expression, cell number, potential for implantation, placental development, embryonic and placental growth velocity, and adult health (32-42). Importantly, multiple large population-based studies now confirm that environmental manipulation associated with IVF significantly increases PE risk and IUGR in humans (RR 2.5 fold) (43-49). Here, we confirm these findings and demonstrate that development of the maternal-fetal transport interface is specifically impaired following IVF in mice and humans, and provide evidence that altered HIF signaling may play a role. Supporting this, we demonstrate increased Hif-2? mRNA but decreased activity in murine IVF conceptuses, likely due to redox stress and impaired mitochondrial bioenergetics, along with subsequent defects in trophoblast differentiation and development of the labyrinthine placenta. We further show that HIF-2? links trophoblast metabolism and differentiation in ways that differ significantly from HIF-1?, and postulate that metabolic reprogramming within the placenta, coupled with impaired transporter gene expression and development of the maternal-fetal transport interface, contribute to fetal growth restriction and PE risk in this setting. Consistent with this, we find that IVF status in human pregnancies is associated with impaired villous development compromising the maternal-fetal transport interface, decreased HIF-2? and Glut-3 expression, and increased PE risk. Based on these observations, we propose to further define HIF-1? and -2? dependent effects on trophoblast differentiation, function and metabolism, how they are impacted by IVF status in rodent models, and the extent to which they contribute to the pathogenesis of ischemic placental diseases in human pregnancies conceived by IVF. The collective expertise of the investigators involved uniquely positions us to advance our understanding of the environmental drivers and metabolic consequences of ischemic placental disease processes, how ART methodologies synergize with them, and to identify novel targets for intervention.